The present invention relates to a fiber optic parametric oscillator and more particularly to a wavelength tunable fiber optic parametric oscillator.
Fiber optic parametric oscillators in the form of a modulational instability laser are known in which all of the pump, signal and idler waves are resonated inside a fiber ring cavity. The operation of this system, however, is undesirably phase sensitive because all three of the waves are resonant. Known fiber optic parametric oscillators have oscillated at the point of modulational instability where the gain of the signal is at a maximum. However, the oscillation frequency can be shifted by only a small amount by changing the pump power. They are therefore, not tunable to a desired frequency over the gain bandwidth.
Further, in known parametric oscillators the parametric response depends on the pump polarization. If the signal polarization drifts towards a polarization state that is orthogonal to the polarization of the pump, the gain of the signal is reduced to a fraction of the maximum gain, achievable when the polarization of the pump and signal are the same.
In accordance with the present invention, the disadvantages of prior fiber optic parametric oscillators have been overcome. The fiber optic parametric oscillator of the present invention is single wave resonant and is tunable over substantially the entire gain bandwidth.
More particularly, the tunable fiber optic parametric oscillator of the present invention includes a fiber parametric amplifier that receives a pump wave and a synchronous signal wave wherein the amplifier separates the pump wave, while amplifying the synchronous signal wave. A spectral filter receives the signal wave from the amplifier, the filter being tunable to reflect a signal wave of a particular wavelength back to the fiber parametric amplifier so as to provide non-degenerate operation of a synchronously pumped fiber optic parametric oscillator.
In one embodiment, the fiber parametric amplifier is in the form of a nonlinear fiber Sagnac interferometer or a nonlinear optical loop mirror having a pump wave port and a signal wave port with a dispersion shifted fiber portion therebetween for amplifying a signal wave having a signal pulse coincident with a pump wave pulse and simultaneously generating an idler wave. The pump wave is reflected back to the pump wave port whereas the signal and idler waves pass through the signal port and are directed to the spectral filter. The spectral filter may be a diffraction grating, or other optical filter that is tunable.
These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.